Prior research efforts have been directed to the discovery of reagents or detector systems for use in passive monitoring devices that are specific either for ozone or nitrogen dioxide. Tin(II)-di-phenylcarbazide solid reagent which has been found to be responsive to both ozone and nitrogen dioxide; Lambert, et al., C. Anal. Latt., 1981, 14, 663; and Lambert, et al., Anal. Chem., 1982, 54, 1227. More recently it was discovered that phenoxazine can be used as a solid monitoring agent for ozone and/or nitrogen dioxide; Lambert, et al., Environ. Sci. Technol., 1987, 21, 503. Phenoxazine reacts to both ozone and nitrogen dioxide but the colors produced are distinctive, a dull brown being formed with ozone and a red-orange with nitrogen dioxide. The search has continued for better and more specific colorimetric detectors for ozone.